Abstract

Nitrogen compounds are important biogeochemical substances that influence the state of water quality. Since transformation of nitrogen compounds is carried out in various water environments (sewage, river, sea and lake waters), it is important to know the rates of these processes. Mathematical models were used for this purpose.

Models for nitrogen compound transformation, including both very simple, purely chemical models and complex ecological models, have already been studied at IIASA (RM-78-34). In this report results from the application of other complex ecological models are presented.

The models are constructed using the principles of biogeocoenosis modeling. The primary objective of this paper is to make a comparative study of the simulation capabilities of different nitrogen transformation models using a given set of experimental data. Modeling results of nitrogen transformation are compared with experimental observations of sewage, river, sea and lake waters. Nitrogen transformations are interpreted from the ecological point of view and are defined by interactions between different microorganisms (bacteria, phytoplankton and zooplankton) and nitrogen compounds (organic and mineral). Two ecological models are presented in this report. It is shown that models constructed on the basis of biochemical compound transformations have broader simulation capabilities than simple models. The model presented here shows good agreement between observed and predicted nitrogen compound concentrations. The model also provides an explanation of the effects of nitrogen transformations on the oxygen content in water environments. However, at present the models discussed cannot be considered entirely adequate for the ecological processes which they describe, although they reproduce in detail the nitrogen transformations in various waters. The absence of multi-aspect experimental observations, specifically carried out for determining the boundaries of model adequacy, impedes the development of applied research on water quality modeling.

The complex ecological models discussed in this report can be used for understanding processes of nitrogen transformations in different water environments. At the same time, these models can also be applied for constructing models of combined biogeochemical cycles of carbon, phosphorus and oxygen, and for simulating functions of aquatic ecosystems as well as for studying various aspects of water quality.